Feebly-interacting particles: FIPs 2020 workshop report

Abstract

With the establishment and maturation of the experimental programs searching for new physics with sizeable couplings at the LHC, there is an increasing interest in the broader particle and astrophysics community for exploring the physics of light and feebly-interacting particles as a paradigm complementary to a New Physics sector at the TeV scale and beyond. FIPs 2020 has been the first workshop fully dedicated to the physics of feebly-interacting particles and was held virtually from 31 August to 4 September 2020. The workshop has gathered together experts from collider, beam dump, fixed target experiments, as well as from astrophysics, axions/ALPs searches, current/future neutrino experiments, and dark matter direct detection communities to discuss progress in experimental searches and underlying theory models for FIPs physics, and to enhance the cross-fertilisation across different fields. FIPs 2020 has been complemented by the topical workshop “Physics Beyond Colliders meets theory”, held at CERN from 7 June to 9 June 2020. This document presents the summary of the talks presented at the workshops and the outcome of the subsequent discussions held immediately after. It aims to provide a clear picture of this blooming field and proposes a few recommendations for the next round of experimental results.

FACET: A new long-lived particle detector in the very forward region of the CMS experiment

“…While searches for such particles in the TeV region continue at the CERN Large Hadron Collider (LHC), the possibility that new particles may be relatively light ( 50 GeV), and yet have escaped detection so far because of very weak coupling to standard model (SM) particles, is receiving considerable attention, as discussed in, e.g., Refs. [1][2][3]. There are many possible so-called portals; these are neutral particles that couple weakly to the SM and also to DM particles (but being unstable are not themselves DM candidates), such as dark photons [4][5][6], heavy neutral leptons [7,8], axion-like particles [9][10][11], and scalars or dark Higgs particles [12,13].…”

Neutrino millicharge and other electromagnetic interactions with COHERENT-2021 data

“…In addition, there are several extensions of the SM that predict new particles with fractional charges [5][6][7][8][9]. The fractionally charged particles are also promising candidates for dark matter [10][11][12][13][14][15]. Even charges of the SM particles can deviate from the integer multiple of 'e/3', where 'e' is the magnitude of unit electric charge.…”

Quasi-Sterile Neutrinos from Dark Sectors I. BSM matter effects in neutrino oscillations and the short-baseline anomalies

“…These constraints can be respected for sufficiently small couplings, and, as evident from (2.7), it is possible to simultaneously keep ∆V nonnegligible if the mediator mass m A D is sufficiently light. Numerous other constraints from colliders, beam dumps, fixed targets, meson decays, stellar cooling, anomalous magnetic dipole moments, etc., also apply in different regions of parameter space of (2.5) [73][74][75][76]. We will, however, defer these considerations to a future work.…”